In recent years, various functions have been required for metallic materials, such as steel materials and alloy materials. More specifically, for example, there is a demand for metallic materials having high processability that can be subjected to complicated processing to manufacture elaborately designed products in the field of metallic materials for use in the manufacture of automotive parts and household electrical appliances.
In general, the processability of a metallic material is greatly affected by the elongation, the work-hardening exponent (n value), and the Lankford value (r-value) of the metallic material. In addition to these factors, the sliding characteristic of a surface of the metallic material also greatly affects the processability of the metallic material. More specifically, a metallic material having a lower surface friction coefficient and a better sliding characteristic has higher processability, and a metallic material having a higher surface friction coefficient and a poorer sliding characteristic has lower processability.
Thus, in order to provide a metallic material having high processability, various methods for surface-treating a metallic material to improve the sliding characteristic of the metallic material surface have been proposed. More specifically, some proposed methods for surface-treating a metallic material to improve the sliding characteristic of the metallic material surface include a method for providing a surface of a high-tensile cold-rolled steel sheet with predetermined roughness using a work roll (see, for example, Patent Literature 1) and a method for forming a predetermined phosphorous oxide film on a surface of a galvanized steel sheet (see, for example, Patent Literature 2).